The present invention relates to a method of recovering enriched radioactive technetium (99mTc) as a radioactive medicine and a raw material for its labeled-compound raw material, and a system therefor.
Tc (technetium) is the transition metal of the atomic number 43 which is situated on the 7th family, the 5th period. Out of the isotopes, 99mTc radiates only γ-ray with the short half-life (6 hours) which suited a diagnostic imaging and the weak energy (140 keV) which suited an external counting. Moreover, 99mTc can be generated by the generator (the 99Mo-99mTc generator) which utilizes a radiation equilibrium with 99Mo and it is used for the nuclear medicine diagnostic imaging. 99mTc is generally used in the way of obtaining it from 99Mo (with the half-life of 66 hours) which is the parent nuclide of 99mTc with a short half-life. Methods for obtaining 99Mo include the Fission method (the nuclear fission method) in which 99Mo with very high specific radioactivity is first generated by the method of uranium nuclear fission, and then separated. In this case, a method of obtaining 99mTc by a milking operation in which the 99mTc is eluted with a physiological saline using alumina as a 99Mo adsorbent, is used as the actual manufacturing technology. On the other hand, there is another method of generating 99Mo using the (n,γ) reaction of the 98Mo isotope which is contained in 99Mo, instead of using uranium as the raw material for obtaining 99Mo. In comparison with the Fission method, this (n,γ) method enables a specific radioactivity of 99Mo to be lowered to about 1/10,000. Therefore, for the practical application of the (n,γ) method, a small amount of 99Tc must be separated, purified and recovered as the daughter nuclide generated from a small amount of 99Mo which is contained in a large amount of Mo. So far, a sol-gel method, MEK method, or a sublimation method are known as the investigated and practically useful (n,γ) method. The inventors of this application have separately proposed PZC method as the (n,γ) method.
JP 2008-102078 A discloses the method and the equipment, in which radioactive molybdenum 99Mo as the parent nuclide of technetium is generated by the 98Mo(n,γ) reaction in a nuclear reactor.
JP 08-309182 A discloses Mo adsorbent for the 99Mo-99mTc generator. And, it is described that this Mo adsorbent is formed by the zirconium-based inorganic polymer which has a high Mo adsorption ability and a high Tc elution performance. This Mo adsorbent is insoluble in water, adsorbs only Mo (including 99Mo) from a water solution which contains Mo (including 99Mo), and elutes 99mTc generated from the radioisotope of 99Mo. Furthermore, this patent literature discloses that a gel of ZrO99MoO4.xH2O is synthesized by reacting Na2Mo(99Mo)O4 obtained by dissolution of Mo(99MoO3) in the (n, γ) method with ZrOCl2 or ZrO(NO3)2, dried, pulverized and packed into a column, and that 99mTc can be eluted from the packed column by a milking operation.
JP 02-54732 A discloses that technetium is eluted from activated carbon which adsorbs and separates technetium from a solution which contains technetium, such as a high radioactive-effluent, or a spent nuclear fuel solution which is generated by reprocessing of a spent nuclear fuel. Technetium in this case is not directed to 99mTc (technetium-99m) with the short half-life for the nuclear medicine diagnostic imaging, but to 99Tc with a very long half-life (technetium 99: the half-life of 21 ten thousand years), which causes a problem of remaining in the nuclear waste.
{Patent Literature 1} Japanese Patent Application Laid-Open No. 2008-102027
{Patent Literature 2} Japanese Patent Application Laid-Open Hei No. 08-309182
{Patent Literature 3} Japanese Patent Application Laid-Open Hei No. 02-54732